Surface functionalization of nanomaterials for improved processing into devices and products

ABSTRACT

Methods for functionalizing the surface of nanomaterials to improve processing and product manufacturing. These methods are useful for oxides, nitrides, carbides, borides, metals, alloys, chalcogenides, and other compositions.

RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10,113,315 filed on Mar. 29, 2002 now U.S. Pat. No. 6,832,735entitled “POST-PROCESSED NANOSCALE POWDERS AND METHODS FOR SUCHPOST-PROCESSING”, which claims the benefit of U.S. ProvisionalApplication No. 60/346,089 Filed on Jan. 3, 2002 the specification ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to nanoscale powders, methodsfor their manufacture, and, more particularly, to post-processing ofnanoscale powders.

2. Relevant Background

Powders are used in numerous applications. They are the building blocksof electronic, telecommunication, electrical, magnetic, structural,optical, biomedical, chemical, thermal, and consumer goods. On-goingmarket demand for smaller, faster, superior and more portable productshas demanded miniaturization of numerous devices. This, in turn, hasdemanded miniaturization of the building blocks, i.e. the powders.Sub-micron and nanoscale (or nanosize, ultrafine) powders, with a size10 to 100 times smaller than conventional micron size powders, enablequality improvement and differentiation of product characteristics atscales currently unachievable by commercially available micron-sizedpowders.

Nanopowders in particular and sub-micron powders in general are a novelfamily of materials whose distinguishing feature is that their domainsize is so small that size confinement effects become a significantdeterminant of the materials' performance. Such confinement effects can,therefore, lead to a wide range of commercially important properties.Nanopowders, therefore, are an extraordinary opportunity for design,development and commercialization of a wide range of devices andproducts for various applications. Furthermore, since they represent awhole new family of material precursors where conventional coarse-grainphysiochemical mechanisms are not applicable, these materials offerunique combination of properties that can enable novel andmultifunctional components of unmatched performance. Commonly-owned U.S.Pat. No. 6,228,904, which along with the references contained therein ishereby incorporated by reference in full, teach some applications ofsub-micron and nanoscale powders. Co-pending application Ser. No.09/638,977, which is assigned to the assignee of the present inventionand which along with the references contained therein is herebyincorporated by reference in full, teaches exemplary methods forproducing high purity nanoscale materials and their applications.

In most applications, powders need to satisfy a complex combination offunctional and processing requirements. Submicron powders in general,and nanoscale powders in particular fail to meet all these requirements.This invention is directed to address these limitations.

Nanoscale powders of various compositions can be produced usingdifferent methods. Some illustrative but not exhaustive lists ofmanufacturing methods include precipitation, hydrothermal processing,combustion, arcing, template synthesis, milling, sputtering and thermalplasma. Often, although not always, nanoscale powders produced by suchmanufacturing methods lead to powders that do meet all the requirementsof an end user application. For example, some of the issues limiting thebroad use of nanopowders include,

1. Nanoparticles tend to form agglomerates that in some ways behave likelarger particles; there is a need for post-processing technologies thatcan recover the nanoparticles from such agglomerates

2. Nanoparticles tend to aggregate thereby making it relativelydifficult to disperse them; there is a need for post-processingtechnologies that can enable ease in the formation of nanoparticulatedispersions in aqueous and non-aqueous solvents

3. Nanoparticles offer unusual combination of properties; howeversometimes they are not used because they are not satisfactory in atleast one of the matrix of performance desired for the application;there is a need for post-processing technologies that can enableimprovement in the unsatisfactory performance at an affordable cost

4. Nanoparticles tend to adsorb significant levels of gases over theirhigh surface areas; alternatively, the surface of nanoparticles are of aform that makes them incompatible with preferred solvents in specificapplications; there is a need for post-processing technologies that canenable improvement in the surface state of nanoparticles to overcomethese limitations

5. Nanoparticles tend to require very high pressures for compaction intoproducts. This is in part because of agglomeration and/or high internalfriction. Although such high pressures can be used to consolidatenanoscale powders, this technique is often limited to the preparation ofthin sections due to very high internal residual stresses.Post-processing techniques are needed that can readily formnanostructured products.

6. Nanoparticles are difficult to process into components because oftheir unusual rheological and other properties. Post-processingtechniques are needed that can enable reliable, reproducible, andaffordable processing of nanopowders into components.

Hence, a variety of needs exist for techniques for improving selectedfeatures of sub-micron powders, and specifically nanopowders, to improvethe performance of these materials in known applications, and to open upnew applications that, until now, were impractical or impossible.

SUMMARY OF THE INVENTION

Briefly stated, the present invention involves the post-processing ofnanoscale powders of oxides, carbides, nitrides, borides, chalcogenides,metals, and alloys are described. The powders are post-processed toimprove their functional and processing characteristics thereby enablingtheir widespread use in commercial applications. Fine powders discussedare of size less than 100 microns, preferably less than 10 micron, morepreferably less than 1 micron, and most preferably less than 100nanometers. Methods for producing such post-processed powders in highvolume, low-cost, and reproducible quality are also outlined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of a process for the continuoussynthesis of nanoscale powders in accordance with the present invention.

FIG. 2 shows an exemplary overall approach for producing submicron ornanoscale powders in accordance with the present invention.

FIG. 3 shows an exemplary overall approach for improving the quality ofsubmicron and nanoscale powders produced in accordance with the presentinvention; and

FIG. 4 shows an exemplary overall approach for post-processed powdersinto a part or component in accordance with the present invention.

FIG. 5 shows an exemplary process for producing a product or device fromnanoscale powders produced in accordance with the present invention; and

FIG. 6 illustrates and exemplary with a porosity gradient through thethickness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed generally at systems and methods forpost-processing of nanoscale powders to alter and improve theirfunctional and processing characteristics to more usefully address theneeds of various applications for the post-processed powders. Inparticular, examples are given of post-processing techniques thataddress agglomeration and aggregation, improve one or more physical,chemical, or solid state properties of the powders, and improve orsimplify the subsequent use of the powders in various applications anddevices. However, the applications of the teachings of the presentinvention are in many cases broader than the specific techniques andsystems taught herein. Accordingly, the basic teachings are readilymodified and adapted to encompass such changes unless specificallytaught otherwise.

To ease understanding of various techniques and concepts taught herein,the following definitions are used in the present specification,although the art recognizes various terms not used herein with similardefinitions, and may define specific words and terms used herein withmore general or more specific meanings:

Definitions

Fine powders, as the term used herein, are powders that simultaneouslysatisfy the following:

-   1. particles with mean size less than 100 microns, preferably less    than 10 microns, and-   2. particles with aspect ratio between 1 and 1,000,000.

Submicron powders, as the term used herein, are fine powders thatsimultaneously satisfy the following:

-   1. particles with mean size less than 1 micron, and-   2. particles with aspect ratio between 1 and 1,000,000.

Nanopowders (or nanosize powders or nanoscale powders or nanoparticles),as the term used herein, are fine powders that simultaneously satisfythe following:

-   1. particles with mean size less than 250 nanometers, preferably    less than 100 nanometers, and-   2. particles with aspect ratio between 1 and 1,000,000.

Pure powders, as the term used herein, are powders that have compositionpurity of at least 99.9%, preferably 99.99% by metal basis.

Powder, as the term used herein encompasses oxides, carbides, nitrides,chalcogenides, metals, alloys, and combinations thereof. The termincludes hollow, dense, porous, semi-porous, coated, uncoated, layered,laminated, simple, complex, dendritic, inorganic, organic, elemental,non-elemental, composite, doped, undoped, spherical, non-spherical,surface functionalized, surface non-functionalized, stoichiometric, andnon-stoichiometric form or substance.

To practice the teachings herein, nanoparticles and sub-micron particlescan be produced by any technique. The preferred techniques includedherein and identified by reference to other patents and patentapplications are provided as examples to ease understanding andimplementation of the invention.

A preferred technique for the present invention is to prepare nanoscalepowders environmentally benign, safe, readily available, high metalloading, lower cost fluid precursors as shown generally in FIG. 1. Theprecursor used in operation 101 may be a gas, sol, single-phase liquid,multiphase liquid, a melt, fluid mixtures and combinations thereof.Illustration of precursors includes but does not limit to metalacetates, metal carboxylates, metal ethanoates, metal alkoxides, metaloctoates, metal chelates, metallo-organic compounds, metal halides,metal azides, metal nitrates, metal sulfates, metal hydroxides, metalsalts soluble in organics or water, metal containing emulsions. Multiplemetal precursors may be mixed if complex powders are desired.

Optionally, precursor 101 is purified by any available technique.Whether a precursor 101 benefits from purification is applicationdependent, and dependent on the original purity of the precursor 101.Another optional, application-specific operation is shown by theaddition of synthesis aids in 107. Synthesis aids may be used to affectphysical, chemical, or solid state properties of the powder produced.Synthesis aids 107 may also act as catalysts or buffers in the processof producing powders.

In the preferred technique, once the desired precursor is available, itis processed at high temperatures in 103 to form the powder 104.Products such as powders 104 produced from these precursors are pure(i.e., having a high degree of homogeneity of one or more desiredproperties such as particle size, particle composition, stoichiometry,particle shape, and the like). It is important that the method ofproducing the product and the environment in which these products areproduced are pure and compatible with the chemistry involved.

The high temperature processing is conducted at step 103 at temperaturesgreater than 1000 K, preferably 2000 K, more preferably greater than3000 K, and most preferably greater than 4000 K. Such temperatures maybe achieved by any method such as, but not limited to, plasma processes,combustion, pyrolysis, electrical arcing in an appropriate reactor. Theplasma may provide reaction gases or just provide a clean source ofheat. A preferred embodiment is to atomize and spray the feed in amanner that enhances heat transfer efficiency, mass transfer efficiency,momentum transfer efficiency, and reaction efficiency. Method andequipment such as those taught in U.S. Pat. Nos. 5,788,738; 5,851,507and 5,984,997 (and which are herewith incorporated by reference) areillustrations of various ways the teachings herein can be practiced.

In the preferred embodiment, the high temperature processing methodincludes instrumentation that can assist the quality control.Furthermore it is preferred that the process is operated to produce finepowders 104, preferably submicron powders, and most preferablynanopowders. The gaseous products from the process may be monitored forcomposition, temperature and other variables to ensure quality at 105.The gaseous products may be recycled at step 106 or used as a valuableraw material when the powders 108 have been formed as determined at step106 in an integrated manufacturing operation.

Once the product fine powders 108 have been formed, it is preferred thatthey be quenched to lower temperatures to prevent agglomeration or graingrowth such as, but not limited to, methods taught in the U.S. Pat. No.5,788,738. It is preferred that methods be employed that can preventdeposition of the powders on the conveying walls. These methods mayinclude electrostatic, blanketing with gases, higher flow rates,mechanical means, chemical means, electrochemical means, orsonication/vibration of the walls.

The product fine powders may be collected by any method. Someillustrative approaches without limiting the scope of this invention arebag filtration, electrostatic separation, membrane filtration, cyclones,impact filtration, centrifugation, hydrocyclones, thermophoresis,magnetic separation, and combinations thereof.

FIG. 2 shows a schematic diagram of a thermal process for the synthesisof nanoscale powders as applied to precursors such as metal containingemulsions, fluid, or water soluble salt. Although a single precursorstorage tank 204 is shown in FIG. 2, it should be understood thatmultiple precursor tanks 204 may be provided and used with or withoutpremixing mechanisms (not shown) to premix multiple precursors beforefeeding into reactor 201. A feed stream of a precursor material isatomized in mixing apparatus 203. The precursor storage 204 mayalternatively be implemented by suspending the precursor in a gas,preferably in a continuous operation, using fluidized beds, spoutingbeds, hoppers, or combinations thereof, as best suited to the nature ofthe precursor. The resulting suspension is advantageously preheated in aheat exchanger (not shown) preferably with the exhaust heat and then isfed into thermal reactor 201 where the atomized precursors are partiallyor, preferably, completely transformed into vapor form.

The source of thermal energy in the preferred embodiments is acombination of heat of reaction in series with a plasma generator 202powered by power supply 206. Plasma gas 207, which may be inert orreactive, is supplied to plasma generator 202 along with any otherdesired process gas 208. Alternatively, the source of thermal energy maybe internal energy, heat of reaction, conductive, convective, radiative,inductive, microwave, electromagnetic, direct or pulsed electric arc,nuclear, or combinations thereof, so long as sufficient to cause therapid vaporization of the powder suspension being processed.

In preferred embodiment, the atomized feed first combusts to form a hotvapor and it is this hot vapor that interacts with the plasma; in thisembodiment, the feed is not directly injected into the plasma.Optionally, in order to prevent contamination of the vapor stream causedby partial sublimation or vaporization, the walls of reactor 201 may bepre-coated with the same material being processed.

The vapor next enters an extended reaction zone 211 of the thermalreactor that provides additional residence time, as needed to completethe processing of the feed material and to provide additional reactionand forming time for the vapor (if necessary). As the stream leaves thereactor, it passes through a zone 209 where the thermokinetic conditionsfavor the nucleation of solid powders from the vaporized precursor.These conditions are determined by calculating the supersaturation ratioand critical cluster size required to initiate nucleation. Rapidquenching and highly concentrated feeds lead to high supersaturationwhich gives rise to homogeneous nucleation. The zones 201, 211, and 209may be combined and integrated in any manner to enhance material,energy, momentum, and/or reaction efficiency.

As soon as the vapor has begun nucleation to form nanoscale clusters,the process stream is quenched in an apparatus within nucleation zone209 to prevent the products from growing or sintering or reachingequilibrium. The quench apparatus may comprise, for example, aconverging-diverging nozzle-driven adiabatic expansion chamber at ratesat least exceeding 1,000 K/sec, preferably greater than 1,000,000 K/sec,or as high as possible. A cooling medium (not shown) may be utilized forthe converging-diverging nozzle to prevent contamination of the productand damage to the expansion chamber. Furthermore, near-sonic velocitiesor supersonic velocities may be employed to prevent collisions betweenthe nanoscale particles. Rapid quenching with high velocities ensuresthat the powder produced is homogeneous in composition, its size isuniform, it is free flowing and the mean powder size remains insubmicron scale.

The quenched gas stream is filtered in appropriate separation equipmentin harvesting region 213 to remove the submicron powder product 308 fromthe gas stream. As well understood in the art, the filtration can beaccomplished by single stage or multistage impingement filters,electrostatic filters, screen filters, fabric filters, cyclones,scrubbers, magnetic filters, or combinations thereof The filterednanopowder product is then harvested from the filter either in batchmode or continuously and then transported using screw conveyors orgas-phase solid transport or other methods known in the art. The powderproduct stream is conveyed to post-processing unit operations discussedbelow.

The purpose of post-processing is to enhance the performance orprocessability of a nanopowder, which may be produced by any syntheticprocess, into a product at an affordable cost. Some of thesepost-processing techniques are discussed below. These post-processingsteps may be done alone or in combination in any order. Quality controltechniques and distributed instrumentation network may be employed atany stage to enhance the performance of nanoscale powders manufactured.

FIG. 3 depicts exemplary equipment that can be used for post-processing.The powders to be post-processed are delivered into a post processingequipment 301. One or more instrument ports such as 302 interfaces apowder quality measurement system to the chamber 301 and to one or moreinstruments 303. The instruments 303 implement methods to measure powderquality, a computer, and a software to control the post processing step.Some non-limiting illustration of instruments 303 include X-raydiffractometer, surface area instrument, laser or light scattering,photo-correlation spectroscopy, angle of repose measurement instrument,imaging instrument, zeta potential instrument, acoustic analysisinstrument, and others. The instrument 303 monitors the quality of thepowders as post-processing progresses and evolves or stops thepost-processing profile in accordance with software settings. Thistechnique can ensure the quality and consistency of the powdersproduced.

In a preferred embodiment, the instrument 303 comprises a system capableof producing an electromagnetic feed signal. This feed signal interactswith the nanoscale particles being processed in chamber 301. The feedsignal after interacting with the particles creates one or more productsignals because of scattering, reflection, diffraction, emission,refraction, transmission, absorption, impedance, or a combination ofthese effects. One or more of these product signals are then received byreceiving part of instrument 303. A resident software installed on acomputing platform then interprets the product signal, mathematicallytransforms it into a numeric quantity if appropriate, compares thenumeric quantity with calibrated responses resident in the instrument,and determines the particle quality at specific time and space. Toillustrate, but not limit, the product signal transformation step canutilize Scherrer analysis of peak broadening detected in a diffractionpattern of electromagnetic waves at specific wavelengths. In some cases,just the peak broadening (or product signal generated) at a specificwavelength may be a sufficient and convenient way for real-time qualitycontrol. In other cases, a reference sample may be employed and thesignal from chamber 301 may be compared against the reference sample todetermine the deviation from the reference sample. When particles aredispersed in a fluid media, lasers may be the preferred electromagneticfeed signal. In yet other cases, sound or ultrasonic waves may beemployed instead of or with electromagnetic waves to establish thepowder quality. Finally, it should be noted that such in-situ qualitycontrol techniques could be employed during nanoscale powder synthesisor post-processing (e.g., in process 106 shown in FIG. 1).

FIG. 4 illustrates in flow diagram form a generalized process forproducing post-processed powders that encompasses the various specificexamples provided herein. The operations shown in FIG. 4 are preferablyperformed in a continuous manufacturing process, however, it iscontemplated that powder production may be performed as a separateprocess from the post-processing operations.

Operations 401 and 402 describe generally operations relating to theinitial manufacture of nanoscale powders, such as by the more specificoperations described in reference to FIG. 1. At 405, the nanoscalepowders are characterized to identify performance limitations. Operation405 typically involves identifying characteristics that are undesirablein a particular application. For example, some applications may tolerateagglomeration, but nevertheless benefit from altering the phase orsurface composition of the powder. Characterization 405 focuses onspecific characteristics desired by an application.

In operation 407, and appropriate post-processing regimen is selectedbased upon the characterization 405 and the desired characteristics ofan application. In each specific example below, post-processingoperation 407 is performed to affect the powder in a particular way.Multiple post-processing operations 407 may be performed to altermultiple characteristics. After powders have been post processed,operation 409, which is similar to operation 405, characterizes thepowder attributes to determine whether characteristics satisfy desiredapplication characteristics. If not, additional post processing can beperformed by returning to operation 407. Otherwise the post-processedpowder, can be used in the desired application at 409.

1. Modify the Degree of Agglomeration:

Nanopowders tend to form agglomerates. These agglomerates tend toadversely affect further processing of nanopowders into usefulnanostructured components. One aspect of the invention involvestechnologies that can prevent and/or address the problem of agglomerateformation. As discussed above, appropriate synthesis can impact theformation of free-flowing nanoscale powders, particle collisions at hightemperatures, and degree of agglomeration. In case nanoscale powdershave undesirable degree of agglomeration, this can be addressed bypost-processing in many cases.

Agglomerates may be of several types. Soft agglomerates are those wherethe neighboring particles forming the agglomerate are weakly attached.Hard agglomerates are those where the neighboring particles forming theagglomerate are sintered to some extent with their neighbors at theirgrain boundaries; such sintering leads to strong chemical bonds betweenthe particles.

Soft agglomerates can be broken down into independent particles byproviding shear forces, or other type of stress, such as those in a ballmill, or jet mill, or other types of mill, or sonication, or impactionof particles on some surface. Other methods that can provide shear orstress can be utilized. It is important that the temperature of theparticles during de-agglomeration be kept below a temperature wheresintering begins. It is suggested that the post-processing of softagglomerates be preferably done at temperatures below 0.5 times themelting point of the substance in Kelvin, more preferably below 0.35times the melting point, and most preferably below 0.25 times themelting point. If necessary, external cooling or cryogenic cooling maybe employed.

In another embodiment, the milling environment is grounded asnanoparticles tend to develop static charge. In yet another preferredembodiment, the milling environment is provided with a fluids such asbut not limiting to organic acid vapors or liquids, alcohols, aldehydes,ketones, aromatics, monomers, amines, and imines. Such an environmentpacifies the surfaces and prevents reformation of soft agglomerates oncethe milling stops.

Hard agglomerates can be post-processed by techniques disclosed for softagglomerates above. However, the energy required for separating sinteredparticles is often significant. Therefore, a preferred method is toprovide a reactive media that can assist separation of the hardagglomerates into independent particles. In a preferred embodiment, asolvent that dissolves the substance being processed is used as thereactive media. Preferably, the reactive media tends to dissolve thesintered interfaces (necks) preferentially and thereby acceleratesstress-induced separation of the particles. The reactive media should beselected such that it does not dissolve the particulates completely. Itshould be noted that such post-processing will lead to dissolution ofthe substance into the media which in turn will change the state of themedia. It is therefore preferred that the post-processing medium bemonitored and refreshed thereby maintaining the preferred environment.To illustrate but not limit, alumina nanoparticles are known to dissolvein highly alkaline solutions. Thus, hard agglomerates comprising aluminananoparticles can be post-processed in a mill and an alkaline medium.The alkaline media is expected to assist the milling process. However,as alumina dissolves, it is expected that the pH of the medium willchange. It is preferred that the media be refreshed, by replacement orrecycle or addition, to a pH that provides desired post-processingperformance.

During the post-processing of hard agglomerates, in another preferredembodiment, the milling environment is provided with appropriate andcompatible surface adhering fluids such as but not limiting to organicacids, alcohols, aldehydes, ketones, aromatics, dispersants, monomers,amines, and imines. Such an environment pacifies the surfaces andprevents formation of agglomerates once the milling stops.

In summary, according to this aspect of the invention, the genericmethod for post-processing agglomerated submicron or nanoscale powderscomprises: (a) synthesizing the powders; (b) determining the nature ofagglomerates; (c) transferring the said agglomerated powders into anequipment; (d) applying shear or other stress to the agglomeratedpowders, commensurate with the determined nature of agglomerate, whilemaintaining the average temperature less than 0.5 times the meltingpoint of the powder in Kelvin for a period sufficient to break theagglomerated powder into de-agglomerated powder; (e) collecting thede-agglomerated powder. This method can further comprise adding areactive media or a surface adhering fluids or both before the shearstep.

2. Modify the Surface:

One of the features of nanoparticles is their high surface area. Thissurface often is covered with functional groups or adsorbed gases orboth. This can cause difficulty in processing the powders into afinished product. In some applications, it is necessary that the surfacebe modified to simplify product manufacturing and to improve theconsistency and reliability of the finished product.

Commonly owned U.S. Pat. No. 6,228,904, incorporated herein byreference, teaches several methods for modifying the surface ofsub-micron and nanoscale powders. Surface modification can beaccomplished in a number of ways. The surface modification may includeone or more of the following steps: (a) the water content on the powdersurface is brought to a desired value followed by a wash of the surfacewith hydrolyzing species (such as but not limiting to organometallics,alkoxides) thereby functionalizing the surface of the powders; (b) thepowder is heated in vacuum to remove adsorbed species; thereafter thepowder is treated to species of choice to cover its surface area; (c)the powder is first washed with an organic acid (such as but notlimiting to oxalic acid, picric acid, acetic acid) which is thenfollowed by a treatment with surface stabilizing species such as but notlimited to nitrogen containing organic compounds, oxygen containingorganic compounds, oxygen and nitrogen containing organic compounds,chalcogenides containing organic compounds, polyalkylimines,polyalkeneimines, and quartemary ammonium species; (d) the powdersurface is reduced or oxidized selectively to form a thin, preferably amonolayer, of functionalized surface. In these methods, the volumefraction of the species or substance that is functionalizing the surfaceis preferably given by:γ_(s)<1/(d _(p)/3+1)

Where, γ_(s) is the volume fraction of the species that isfunctionalizing the nanomaterial surface and d_(p) is the average domainsize of the nanomaterial in nanometers. While the above equation is thepreferred guideline, higher volume fractions may be utilized for certainapplications. The motivation for these and other surface modificationpost-processing steps is to produce an interface that makes thenanoscale powders easier to process or easier to include as aconstituent in the final product while retaining the benefits ofnanoscale dimensions in the final product.

As a particular example, nanoscale silica particles can be surfacetreated with organosilicon compounds. For example, hexamethyldisilazaneis used to make silica surface hydrophobic. The hydrophobicity resultsfrom the treatment with hexamethyldisilazane, which replaces many of thesurface hydroxyl groups on the silica nanoparticles with trimethylsilylgroups. One aspect of the present invention involves the selection ofthe composition of the species chosen to treat the surface of ananopowder in a manner that enhances the performance of the treatedpowder. While the prior art methods can be utilized for the purposes andmotivations outlined in this specification, it is preferred that thecomposition of the species that is functionalizing the nanomaterialsurface be chosen to enhance the performance of the treated powder. Inmajority of cases, a non-silicon composition is anticipated to bepreferred for surface treatment.

3. Modify the Near-Surface Composition:

As mentioned above, one of the features of nanoparticles is their highinterface area. The performance of a nanostructured product preparedfrom nanoscale powders is therefore strongly affected by the performanceof the interface. Some non-limiting illustrations of interface influenceon the performance of a nanostructured product includes the highinterface diffusivity, electrochemical properties, phonon pinning,catalytic properties, optical properties, and size-confined electricaland thermoelectronic properties. A post-processing step that can modifythe interface composition can significantly impact the performance ofthe product that comprises such nanoscale powders.

One method for modifying the near-surface composition is to partiallyreduce the composition. For example, an oxide nanopowders if treatedwith hydrogen or ammonia or carbon monoxide or methanol vapors atmoderate temperatures for a pre-determined time can lead to a powdercomposition where surface of the nanopowder is deficient in oxygen whilethe bulk retains full stoichiometry. Similarly, if the nanoscale powderis treated with methane in the presence of carbon, the surface of thenanopowder can be transformed into an oxycarbide or carbide, while thecore of the particle remains an oxide. Alternatively, carbothermicnitriding conditions can be used to produce nitride rich surfacecomposition. It is important that carbothermic nitriding be done in thepresence of a stoichiometrically excess of carbon to prevent excessivecoarsening and sintering of the particles. Boron rich surfacecompositions can be achieved by carbothermic reduction in presence ofborane or other boron containing compounds. It should be noted thatthere is no need to completely change the composition of the nanoscalepowder. The benefits of improved performance can be achieved by forminga nanoscale powder with a composition gradient, i.e., where the surfaceis of one desired composition (stoichiometric or non-stoichiometric),the core of the particle is of another desired composition(stoichiometric or non-stoichiometric), and the particle's compositiontransitions from the core to that at the surface.

Yet another embodiment of the current invention is to use mechanicallyfused coatings on submicron or nanoscale powders to change the surfacecomposition. This approach essentially involves high shear mixing wherethe shear energy is high enough to fuse one composition on the surfaceof the other. This approach can significantly impact the flowability,angle of repose, shape, physical and chemical property of the compositeparticle. Furthermore, this approach can produce powders withcharacteristics that are not achievable by either of the powders aloneor by a simple non-fused blend of the powders.

Yet another embodiment of the current invention is to coat the submicronor nanoscale powders with another material followed by heat treating theparticle to induce chemical reaction(s) that change the surfacecomposition. This process, for illustration, can comprise (a) coatingsubmicron or nanoscale particles with an organic or inorganic ormetallorganic substance, (b) placing the particles in an equipment wherethe said powders can be heated in an environment of desired pressure,temperature, and gas composition, (c) heating the particles through alinear or non-linear temperature profile, (d) holding the particles atdesired temperatures for a suitable length of time, (e) cooling theparticles to room temperature, and (f) removing the particles from theequipment and using it in a suitable application. These steps canfurther comprise steps where suitable instruments are employed tomonitor and control the feed, or process, or products, or a combinationof these. It is expected that such heat treated of coated particles canmodify the near-surface composition of the particles and therefore theirperformance.

4. Modify the Phase:

Post-processing can be used to modify the phase of nanoparticles. Thephase of the particle affects its performance and such post-processingcan therefore be useful. For example, thermal treatment (cryogenic orhigh temperature) of an oxide can be used to change an orthorhombic ortriclinic or monoclinic phase to cubic phase. Alternatively, anatasephase can be changed to rutile phase or reverse. Pressure can becombined with thermal treatment to achieve phase change.

Another embodiment of this invention is to use electrical current tomodify the phase of the material. While not exclusively limited toconducting materials, electrical transformation can be particularlysuitable in conducting materials (oxides, non-stoichiometric materials,non-oxides) since electrical current can also provide nominal levels ofohmic heating. Similarly magnetic field can be used to modify the phaseof a material.

5. Modify the Surface Area of the Particles

One of the motivating factors for using nanoparticles is their uniquesurface area. Often, the surface area of the powder is dependent on theprocessing method and processing conditions used to produce the powders.Techniques that can enhance the surface area of a low surface areapowder can make the powder more desirable in certain applications. Thisis often difficult to do.

In one embodiment aiming to engineer the particle surface area, theparticles are produced with another sacrificial compound that retainsits identity. The sacrificial compound is then removed by extraction ordissolution into a suitable medium. For example, zinc oxide can beco-synthesized with zirconium oxide followed by dissolution of zincoxide in a medium of suitable pH. The zinc oxide can be recycled toreduce the cost of the nanoparticle manufacture. This process, in moregeneric sense, can be described as a method for increasing the surfaceof submicron or nanoscale particles comprising (a) mixing the precursorfor submicron or nanoscale particles desired with a precursor ofsacrificial composition, (b) synthesizing and collecting the particlesas a composite of the desired particle composition and the sacrificialcomposition, (c) extracting the sacrificial composition using a suitablesolvent from the composite particle to achieve the desired surface area,(d) if desired, washing the particles to remove traces of solvent, and(e) if desired, further post-processing the particles to meet customerrequirements. Some illustrations of such sacrificial compositionsinclude zinc oxide, magnesium oxide, calcium oxide, alkaline metaloxides, tin oxide, antimony oxide, indium oxide, multi-metal oxides,chalcogenides, halides, and water soluble salts.

In another embodiment, the particles of desired composition are producedwith another sacrificial metal or alloy that retains its identity in thecomposite particle. The sacrificial metal or alloy is then selectivelyremoved by extraction or dissolution into a suitable medium as explainedabove. Some illustrations of such sacrificial compositions includetransition metals, semi-metals, and various alloys.

In some cases, it is possible that the particles of desired compositionmay by themselves be soluble in a solvent. In these cases, the surfacearea of the particles can be modified by direct dissolution in asuitable solvent for appropriate period of time. In yet anotherembodiment, the submicron or nanoscale particles may be milled in asolvent to modify the surface area or other characteristics of theparticles. It all cases, it is preferred that the solvent used fordissolution process is replenished to maintain the best dissolutionkinetics. The replenishment can be achieved by removing, recovering andrecycling the solvent. It is also preferred that the dissolution processconditions such as temperature and mixing rates are engineered andinstrumented for high productivity.

In another embodiment, instead of using a sacrificial composition thatcan be removed using a solvent, a sacrificial composition that can beremoved by sublimation may be preferred. For this embodiment, compoundsor metals or alloys with high vapor pressures at moderate temperatures,such as less than 975K, are preferred. In this embodiment, vacuum may beemployed to reduce the time needed to sublime the sacrificialcomposition.

6. Modify the Shape

One of the desirable features in particle technology is the ability tocontrol particle shape. Quite often, the shape of very small particlesis spherical. However, a number of applications prefer particles with anaspect ratio greater than 1.5, more preferably greater than 3.0, andeven more preferably greater than 10.0. Techniques that can modify theshape of a particle can also enhance the surface area of a powder.

One post-processing technique for modifying shape is catalytictransformation. This process, in more generic sense, can be described asa method for modifying the shape of submicron or nanoscale particlescomprising (a) mixing the submicron or nanoscale particles or theirprecursors with a catalyst that preferentially favors dissolution andprecipitation of the particles, (b) processing the mixture at atemperature greater than 300K, preferably greater than 1000K (c)collecting the particles with desired aspect ratio, and (d) if desired,further post-processing the particles to meet customer requirements. Inthis embodiment, the catalytic reactions are preferably conducted in agas phase.

Another post-processing technique for modifying shape is the use ofshear at temperatures where the material softens. As a rule of thumb,this temperature for many composition is between 0.2*T_(m) and0.95*T_(m), where T_(m) is the melting point of the composition inKelvin.

Yet another post-processing technique for modifying shape is to mix theparticles in a polymer followed by thermal treatment of the mix. Thethermal treatment is anticipated to cause sintering and growth of theparticle into particle shapes of desired aspect ratio. Techniques suchas extrusion may be employed before the thermal treatment to control theaspect ratio of the particles.

Still another post-processing technique for modifying shape is todeposit the submicron or nanoscale particles in a template followed bythermal treatment between 0.2*T_(m) and 0.95T_(m), where T_(m) is themelting point of the composition in Kelvin. Illustrative templatesinclude anodized aluminum, anodized silicon, other anodized metals,micro-machined templates, porous polymers, radiation templated polymers,zeolites, emulsion produced templates, and other templates. The templatecan be removed using solvents and other techniques after the desiredaspect ratio particles have been produced.

7. Post-Processing of Nanopowders to Achieve Consolidation

Once the nanoscale powders have been post-processed, they may betransformed into a useful product. For example, coatings, casting,molding, compacting, spraying, pressing, electrodeposition, and othertechniques followed by thermal treatment for consolidation and sinteringare exemplary techniques for manufacturing or forming useful productsfrom post-processed powders in accordance with the present invention.

One illustrative method is carefully controlled slurry processing.Briefly, the slurry process entails the dispersion of powders in aliquid medium that contains a solvent, as well as organic constituentsadded to tailor the theological properties of the dispersion and themechanical properties of the product after the solvent is removed bydrying. The solvent can be aqueous or non-aqueous; many slip systems areformulated with organic solvents including alcohols, ketones, andhydrocarbons. Dispersants are an important additive since they preventagglomeration and coagulation of the powders in suspension. Dispersioncan be facilitated by steric repulsion, meaning adsorbed moleculesphysically interfere with those of other particles, or electrostaticrepulsion, which employs the repulsive nature of particles with asimilar surface charge. Commonly employed chemical dispersants arecarboxylic acids and phosphate esters for solvent-based systems. Inpractice, most systems are stabilized by a combination of electrostaticand steric mechanisms.

Dispersing nanopowder slurries is not a trivial process. Agglomerationin slip systems causes problems similar to those that occur as a resultof agglomeration in dry pressing. In this case, however, theagglomerates can be broken by the application of aggressive forcesduring processing. Exemplary methods that can be utilized are ballmilling, high power ultrasonic agitation, or shear homogenization.Applying these processes to powder suspensions can lead to a green body(i.e., unfired) with a very high density (i.e., >65%); this body, inturn can be sintered to near theoretical density.

FIG. 5 illustrates this aspect of the disclosed invention schematically.The details of the invention are as follows:

A. Nanocrystalline ceramic powder produced in 501 and is formulated intoa slurry, slip or ink in 503. An illustration of preferred embodiment,but in no way limiting the scope of this invention, is as follows: 10vol. % nanocrystalline SiC powder, a cationic dispersant in the level 2mg/m², a polymeric binder, and toluene are ball-milled with zirconiamedia in a polyethylene bottle for 12 hours.

B. The slip is tape-cast in 505 into a layer, preferably 0.1 to 1000microns thick, more preferably that is 1 to 100 microns thick, and mostpreferably that is 5-50 microns thick.

C. Multiple sheets or layers produced in 505 are stacked to yield thedesired thickness, and the layers are laminated together.

D. The laminated layers are sectioned in 507 to yield the appropriatecomponent geometry. In operations 509 and 511, the sectionals can bestacked in a desired order, and pressed and cured to form a workingstructure.

E. The component is placed in a furnace and sintered in operation 513,when appropriate, to full density (e.g., 1400° C. for zirconia).Operation 513 yields a device, part or component that can then beprocessed through various finishing operations 515 such as polishing,terminating, electroding, passivating, packaging, or otherdevice-specific processes.

Distinctive features of this invention relate to the quality of thefinal product and the low-cost and flexibility of the processing. Usingmultiple tape cast layers allows layers to be formed in a wide varietyof shapes and sizes using inexpensive and efficient equipment. Activelayers (i.e., layers comprising materials designed to perform a specificdevice function) can be intermixed with non-active layers that providestructural support, electrical or mechanical connectivity, and othersupporting functions. Stacking tape cast layers into laminate structuresallows control over device shape in three-dimensions. A differentiatingfactor of the proposed invention, over prior art, is the benefit of ananocrystalline structure in the finished product.

The advantages of nanomaterials such as increased hardness andwear-resistance, novel electrical properties, electrochemicalproperties, chemical, thermal, magnetic, thermoelectric, sensing,optical, electro-optical, display, energetic, catalytic, and biologicalproperties will benefit many engineering applications.

Possible compositions of the active layer include but are not limited toorganic, inorganic, metallic, alloy, ceramic, conducting polymer,non-conducting polymer, ion conducting, non-metallic, ceramic-ceramiccomposite, ceramic-polymer composite, ceramic-metal composite,metal-polymer composite, polymer-polymer composite, metal-metalcomposite, processed materials including paper and fibers, and naturalmaterials such as mica, dielectrics, ferrites, stoichiometric,non-stoichiometric, or a combination of one or more of these.Illustrative compositions include but are not limited to doped orundoped, stoichiometric or non-stoichiometric titanium oxide, bariumtitanate, strontium titanate, zinc oxide, zinc sulfide, indium oxide,zirconium oxide, tin oxide, antimony oxide, tungsten oxide, molybdenumoxide, tantalum oxide, cerium oxide, rare earth oxides, silicon carbide,haftium carbide, bismuth telluride, gallium nitride, silicon, germanium,iron oxide, titanium boride, zirconium boride, zirconates, aluminates,tungstates, carbides, manganates, ruthenates, borates, hydrides, oxides,oxynitrides, oxycarbides, halides, silicates, phosphides, nitrides,chalcogenides, complex oxides such as dielectrics and ferrites.

Additionally, the active layer can be porous or dense, flat or tapered,uniform or non-uniform, planar or wavy, straight or curved,non-patterned or patterned, micron or sub-micron, grain sized confinedor not, or a combination of one or more of these.

The solvent for the slip can be organic, inorganic, emulsion, aqueous,acidic, basic, neutral, charged, uncharged, stable or metastable. Thestacking can be manual, automatic, computer aided, optically aligned, orrobotically aligned.

In one embodiment, the slip, slurry, or ink can comprise nanoscalepowders only along with the solvent. In another embodiment, the slip,slurry, or ink can comprise can be a mixture of nanoscale powders,submicron, and micron sized powders. In yet another embodiment, theslip, slurry, or ink can comprise nanoscale powders as dopants. The mixmay be heterogeneous or homogeneous, the latter being preferred. For thescope of this invention, the slip, slurry, or ink has greater than 0.01%of its total solids as added nanoscale size powders.

The tapes can be stacked in any pattern. The device may just have onelayer or multiple layers, the preferred embodiment being multiplelayers. The individual layers can be the same or different formulation.Additionally, it is possible to replace or combine one of the activelayers with a layer capable of a secondary but desired function. Forexample, one or more of the layers can be replaced with resistive layersby design to provide heat to the device or component. In some situationsit may be desirable to have one or more active layers replaced with EMI(electromagnetic interference) filter layers to minimize noise byinductively or capacitively coupling with the active layer. In anothersituation, one of the layers can be air or an insulating layer in orderto provide thermal isolation to the active layer. In yet anothersituation, sensing layers may be provided sense the temperature ordensity or concentration of one or more species in the feed or processedor recycle stream. In yet another situation, electrochemical couplelayers may be provided to internally generated electricity and energyneeded to satisfactorily operate the device. In other conditions, theelectrode layers can be provided to function as anodes and cathodes. Insome situations, the device may be a minor part of the multilaminatedevice and the device containing device can have primary function ofreliably providing an electrical, thermal, magnetic, electromagnetic,optical, or structural function in an application. The layers can alsocomprise multilaminates of different material formulations. Thesedifferent formulations can have different properties that allow thefabrication of a functionally graded material (FGM).

The multilayer stack may have a rectangular shape. However, the stackshape can also be circular, elliptical or any other shape. Additionally,the edges may be rounded or sharp. The product could be finished,polished, cut, plated, terminated, rounded, radiatively treated, orprocessed further with the motivation to improve properties or to impartnew performances.

8. Uses

Applications provided by this invention include: surgical blades,cryogenic slicing, blades for cutting polymers and fabrics, blades forscissors, utility knives, hunting knives, snap knives, and art & hobbyknives. Ceramic blades are currently being proposed in theaforementioned applications due to the fact that they outwear steelknives 50-100 times and carbide knives 7 to 10 times. The cost driversfor blades used in industrial applications is quite high due to the factthat the downtime associated with replacing a blade is more costly(i.e., non-productive downtime) than the material for the blade. Thisinvention proposes to leapfrog the current technology by reducing costs,and by extending the performance of the part and the lifetime of theblades significantly. Any structural components could be manufacturedusing this invention with the motivation to reduce cost, increasevolume, and/or improve performance. Additional applications includeceramic, metal, or composite seals. These low-profile components can befabricated by a multi-layer build-up process described in FIG. 5.

An additional application of the teachings herein is functionally gradedparts or components that are dense or porous. Illustration includes afilter with a porosity gradient through the thickness as shown in FIG.6, for example. In the filter application shown in FIG. 6, a relativelythick porous substrate 601, an intermediate porosity layer 602, and ananocrystalline layer 603 having low relative porosity comprise similarmaterials, and may use a single powder composition as a startingmaterial. Post-processing techniques described herein are used to alterthe porosity of the powder as it is deposited or formed on the precedinglayers using, for example, the slurry processing techniques describedabove.

This invention is contemplated to have application in the biomedicalfield, among other fields. For example, the present invention may beapplied to producing implant materials, monitors, sensors, drug deliverydevices, and biocatalysts from nanoscale powders using the multi-layerlaminating process to produce three-dimensional shapes.

This invention may also be applied the solid oxide fuel cell (SOFC)area. Zirconia is one of the materials that has been investigated as thesolid electrolyte for SOFC's. Solid electrolyte components can be madeby tape casting multi-layer devices with a very high surface area (i.e.,nanomaterial based electrolytes).

Additionally, the post-processed nanopowders made in accordance with thepresent invention may be used to produce electrical devices such asvaristors, inductors, capacitors, batteries, EMI filters, interconnects,resistors, thermistors, and arrays of these devices from nanoscalepowders. Moreover, magnetic components such as giant magnetoresistiveGMR devices may be manufactured from nanoscale powders produced inaccordance wit the present invention as well as in the manufacturethermoelectric, gradient index optics, and optoelectronic componentsfrom nanoscale powders.

The teachings in this invention are contemplated to be useful inpreparing any commercial product from nanoscale powders whereperformance is important or that is expensive to produce or is desiredin large volumes. Moreover, post-processed fine powders have numerousapplications in industries such as, but not limiting to biomedical,pharmaceuticals, sensor, electronic, telecom, optics, electrical,photonic, thermal, piezo, magnetic, catalytic and electrochemicalproducts. Table 1 presents a few exemplary applications ofpost-processed powders.

TABLE 1 Post-processed Ceramic Nanopowder Application CompositionCapacitors, Barium titanate, strontium titanate, barium strontiumResistors, Inductors, titanates, silicates, yttria, zirconates,nanodopants, Integrated Passive fluxes, electrode formulationsComponents Substrates, Alumina, aluminum nitride, silicon carbide,Packaging cordierite, boron carbide, composites Piezoelectric PZT,barium titanate, lithium titanates, nanodopants transducers MagnetsFerrites, high temperature superconductors Electroptics(Pb,La)(Zr,Ti)O₃, nanodopants Insulators Alumina Varistors ZnO, titania,titanates, nanodopants Thermistors Barium titanates, mangnates,nanodopants Fuel Cells Zirconia, ceria, stabilized zirconia,interconnects materials, electrodes, bismuth oxide, nanodopantsMechanical Silicon nitride, zirconia, titanium carbide, titaniumcomponents, nitride, titanium carbonitride, boron carbide, boronsealants, adhesives, nitride, dispersion strengthened alloys gaskets,sporting goods, structural components Biomedical Aluminum silicates,alumina, hydroxyapatite, zirconia, zinc oxide, copper oxide, titaniaCoatings Indium tin oxide, nanostructured non-stoichiometric oxides,titania, titanates, silicates, chalcogenides, zirconates, tungstenoxide, doped oxides, concentric coated oxides, copper oxide, magnesiumzirconates, chromates, oxynitrides, nitrides, carbides, cobalt dopedtitania Pigments Oxynitrides, titania, zinc oxide, zirconium silicate,zirconia, doped oxides, transition metal oxides, rare earth oxidesEngineered plastics Silicates, zirconates, manganates, aluminates,borates, barytes, nitrides, carbides, borides, multimetal oxidesCatalysts Aluminum silicates, alumina, mixed metal oxides, zirconia,metal doped oxides, zeolites Abrasives, Aluminum silicates, zirconiumsilicates, alumina, Polishing Media ceria, zirconia, copper oxide, tinoxide, zinc oxide, multimetal oxides, silicon carbide, boron carbide

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the claims.

9. EXAMPLE 1

The following batch was mixed:

MATERIAL DESCRIPTION AMOUNT (Vol. %) SiC NRC powder 10 A 203 Dispersant3.3 B74001 (solids) Binder 10.4 B74001 (liquid) Binder 8.5 TolueneSolvent 77.8

The mixture was milled with zirconia media for 12 hours in apolyethylene bottle. After milling, the slip was removed from the bottleand tape cast (Model #101, Drei-Tech Corporation) through a 165 microngap doctor blade. The final thickness of the tape after drying wasapproximately 30 microns. A total of 33 layers of tape were stacked andtacked (Model #NT300, Pacific Trinetics Corp., San Marcos, Calif.) underSiC blades. The layers were then laminated together at a temperature ofapproximately 65° C. at a pressure of 26.7 MPa in an isostaticlamination system (Model #IL-4004, Pacific Trinetics Corp., San Marcos,Calif.). The binders were burned out in nitrogen (Model #Inert Gas Oven,Blue M Electric, Watertown, Wis.) with the following schedule: 2° C./minto 200° C. for 1 hour, and 1° C./min to 550° C. for 6 hours.

The laminated material was sectioned with a commercially available razorblade into the approximate geometry of the finished blade. An edge wasput into the SiC blade by sandwiching it between two pieces of stainlesssteel and holding it at an angle of 45 degrees (see FIG. 1) whilerunning it across SiC abrasive paper (1200 grit).

10. EXAMPLE 2

The following batch was mixed:

MATERIAL DESCRIPTION AMOUNT (Vol. %) SiC Superior Graphite 059 10 A 203Dispersant 1.1 B74001 (solids) Binder 12.2 B74001 (liquid) Binder 20.9Toluene Solvent 55.8

The balance of the process was conducted in accordance with Example 1.

11. EXAMPLE 3 Thermistor

Nanoscale barium titanate slip is prepared. An ink of nickel isprepared. A tape of barium titanate is formed. The tape is sliced intosections and electrode applied on one surface. Alternating stacks oftitanate and nickel electrode are placed to form a multilayer structure.The laminate is cured and then diced into multilayer PTC thermistorelements. The elements are sintered into dense structure and thenterminated. The resulting device is used to control and monitortemperature. Alternatively, they are used as electromagnetic energylimiting devices. In another example, the titanate powder can bereplaced with nanoscale manganate powder to form an NTC multilayerthermistor.

Although the invention has been described and illustrated with a certaindegree of particularity, it is understood that the present disclosurehas been made only by way of example, and that numerous changes in thecombination and arrangement of parts can be resorted to by those skilledin the art without departing from the spirit and scope of the invention,as hereinafter claimed.

1. A method for functionalizing the surface of nanomaterials comprising:washing nanomaterials comprising soft agglomerates with an organic acid;treating the washed nanomaterials with a surface stabilizing speciesselected from the group consisting of: nitrogen containing organiccompounds, oxygen containing organic compounds, oxygen and nitrogencontaining organic compounds, chalcogenide containing organic compounds,polyalkylimines, polyalkeneimines, and quaternary ammonium species; andwherein the treatment step functionalizes the surface of thenanomaterials by creating a layer on the surface of the nanomaterials;wherein the layer has a volume fraction that is given by therelationship:γ_(s)<1/(d _(p)/3+1) wherein, γ_(s) is the volume fraction of thesurface stabilizing species and d_(p) is the average domain size of thenanomaterials measured in nanometers.
 2. The method of claim 1 whereinthe nanomaterials comprise a substance selected from the groupconsisting of: oxides, carbides, nitrides, chalcogenides, metals, andalloys.
 3. The method of claim 1 wherein the surface stabilizing speciescomprises a non-silicon composition.
 4. A method for functionalizing thesurface of nanoparticles comprising: contacting nanoparticleagglomerates comprising hard agglomerates with a reactive media thatdissolves sintered interfaces between the agglomerated nanoparticles;applying stress to the agglomerates for a period sufficient to break upthe agglomerates; heating the nanoparticles thereby removing adsorbedspecies on the nanoparticles; treating the heated nanoparticles with aspecies to functionalize the surface of the nanoparticles; and whereinthe reactive media accelerates stress-induced separation of agglomeratedparticles, and the treatment step functionalizes the surface of thenanoparticles with the species.
 5. The method of claim 4 wherein theheating step is aided by the presence of vacuum.
 6. The method of claim4 wherein the nanoparticles comprise a substance selected from the groupconsisting of: oxides, carbides, nitrides, chalcogenides, metals, andalloys.
 7. The method of claim 1 wherein the nanomaterials comprise apurity greater than 99.9% by metal basis.
 8. The method of claim 4wherein the nanomaterials comprise a purity greater than 99.9% by metalbasis.
 9. The method of claim 1 wherein the nanomaterials comprise anaspect ratio greater than
 1. 10. The method of claim 4 wherein thenanomaterials comprise an aspect ratio greater than 1.